JP3448196B2 - Nitride semiconductor light emitting device - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to a nitride semiconductor (In _X A
l _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1),
The present invention relates to a nitride semiconductor light emitting device used as a light emitting device such as a light emitting diode device and a laser diode device.

[0002]

2. Description of the Related Art Nitride semiconductors are high brightness pure green light emitting LEs.
As D and blue LEDs, they have already been put to practical use in various light sources such as full-color LED displays, traffic lights, and image scanner light sources. These LED devices basically include a buffer layer made of GaN on a sapphire substrate,
An n-side contact layer made of Si-doped GaN, an active layer made of InGaN having a single quantum well structure, a p-side clad layer made of Mg-doped AlGaN, and Mg-doped Ga.
It has a structure in which a p-side contact layer made of N is sequentially laminated, and at 20 mA, a blue LED having an emission wavelength of 450 nm is 5 mW, and external quantum efficiency is 9.1% and 520 n.
m green LED shows excellent characteristics of 3 mW and external quantum efficiency of 6.3%.

Further, the applicant of the present invention announced the laser oscillation of 410 nm at room temperature under pulse current using this material for the first time in the world (for example, Jpn.J.Appl.Phys.35 (1996) L74, Jp.
nJAppl.Phys.35 (1996) L217 etc.}. This laser element
Multiple quantum well structure using InGaN (MQW: Multi-
Quantum-well) double hetero structure having an active layer, threshold current 610 mA, threshold current density 8.7 kA / cm ² , 4 under the condition of pulse width 2 μs and pulse period 2 ms.
Oscillation of 10 nm is shown. In addition, the present applicant has also succeeded in continuous oscillation at room temperature for the first time and announced. {For example, Nikkei Electronics December 2, 1996 Technical Bulletin, Appl.Phys.L
ett.69 (1996) 3034-, Appl.Phys.Lett.69 (1996) 4056-
Etc., this laser device exhibits a continuous oscillation of 27 hours at a threshold current density of 3.6 kA / cm ² , a threshold voltage of 5.5 V, and a power of 1.5 mW at 20 ° C.

[0004]

As described above, nitride semiconductors have already been put to practical use in LEDs, and LDs have reached continuous oscillation for several tens of hours. However, LEDs are used as a light source for illumination, an outdoor display exposed to direct sunlight, for example. In order to achieve equality, further improvement in output is required. Further, in the LD, further improvement is required in order to reduce the threshold value to make the life longer and to put the LD into practical use as a light source such as an optical pickup. Further, the LED element has Vf of 3. at 20 mA.
It is near 6V. By further reducing Vf, the amount of heat generated by the element is reduced, and the reliability is improved. In the laser device, lowering the voltage at the threshold is very important for improving the life of the device. The present invention has been made in view of such circumstances, and an object of the present invention is mainly to improve the output of nitride semiconductor elements such as LEDs and LDs and to reduce Vf to improve the reliability of the element. Is to improve the sex.

[0005]

A first nitride semiconductor light emitting device according to the present invention comprises an undoped first nitride semiconductor layer and an n-type impurity between a substrate and an active layer in order from the substrate side. A second nitride semiconductor layer of n-conductivity type doped with
A nitride semiconductor having an undoped third nitride semiconductor layer, and having a buffer layer grown between the substrate and the first nitride semiconductor layer at a temperature lower than that of the first nitride semiconductor layer. In the light emitting device, the second nitride semiconductor layer has a superlattice structure, an n-electrode is formed on the second nitride semiconductor layer, and the third nitride semiconductor layer is InGaN.
Is characterized in that. Note that the undoped nitride semiconductor layer in the present invention refers to a nitride semiconductor layer that is not intentionally doped with impurities, for example, impurities contained in raw materials, contamination in a reactor, and other layers intentionally doped with impurities. In the present invention, a layer in which impurities are mixed by unintended diffusion and a layer that can be regarded as substantially undoped due to a slight amount of doping (for example, a resistivity of 3 × 10 ⁻¹ Ω · cm or more) are also defined as undoped. The superlattice layer refers to a multilayer film structure in which nitride semiconductor layers having a film thickness of 100 angstroms or less, more preferably 70 angstroms or less, and most preferably 50 angstroms or less are laminated. In the first nitride semiconductor light emitting device of the present invention, the third nitride semiconductor layer has an In mixed crystal ratio y of 0.1 or less.
It is preferably _y Ga _1-y N. A second nitride semiconductor light emitting device according to the present invention is characterized in that between a substrate and an active layer,
An undoped first nitride semiconductor layer in order from the substrate side;
an n-conductivity type second nitride semiconductor layer doped with an n-type impurity; and an undoped third nitride semiconductor layer,
A nitride semiconductor light emitting device having a buffer layer grown between the substrate and the first nitride semiconductor layer at a temperature lower than that of the first nitride semiconductor layer, the second nitride semiconductor The layer has a superlattice structure, an n-electrode is formed on the second nitride semiconductor layer, and the resistivity of the second nitride semiconductor layer is less than 8 × 10 ⁻³ Ω · cm and 1 × 10 ^−5. Ω · cm or more, and the first nitride semiconductor layer is AlGaN. Moreover, in the second nitride semiconductor light emitting device according to the present invention, it is preferable that the first nitride semiconductor layer is Al _X Ga _{1 -X} N having an X value of 0.2 or less. Further, according to the third nitride semiconductor light emitting device of the present invention, between the substrate and the active layer, an undoped first nitride semiconductor layer is sequentially provided from the substrate side, and an n-conductivity type doped with an n-type impurity. Of the second nitride semiconductor layer and a third nitride semiconductor layer having a resistivity higher than that of the second nitride semiconductor layer, and between the substrate and the first nitride semiconductor layer. A nitride semiconductor light emitting device having a buffer layer grown at a temperature lower than that of the first nitride semiconductor layer, wherein the second nitride semiconductor layer has a superlattice structure and the second nitride semiconductor layer has a superlattice structure. An n-electrode is formed on the layer, and the second nitride semiconductor layer has a resistivity of less than 8 × 10 ⁻³ Ω · cm and 1 × 10 ^−5.
It is characterized by being Ω · cm or more. Third according to the present invention
In the above nitride semiconductor light emitting device, the third nitride semiconductor layer may be GaN or InGaN. In the third nitride semiconductor light emitting device according to the present invention, the first nitride semiconductor layer may be GaN or AlGaN.

In the present invention, the resistivity of the second nitride semiconductor layer is preferably less than 8 × 10 ⁻³ Ω · cm, and the resistivity of the second and third nitride semiconductor light emitting devices is within this range. did. The resistivity of the second nitride semiconductor layer is 8 × 10
^When it becomes ^-3 Ω · cm or more, Vf tends not to decrease so much. The more preferable range of the resistivity is 6 × 10 ⁻³ Ω ·
cm or less, more preferably 4 × 10 ⁻³ Ω · cm or less. The lower limit is preferably adjusted to 1 × 10 ⁻⁵ Ω · cm or more, and is set in this range for the second and third nitride semiconductor light emitting devices. When the second nitride semiconductor layer is formed as a single layer, the lower limit value is preferably 1 × 10 ⁻³ Ω · cm or more, but when the second nitride semiconductor layer is formed as a superlattice layer, Is preferably adjusted to 1 × 10 ⁻⁵ Ω · cm or more. If the resistance is lower than the lower limit, the amount of impurities such as Si, Ge, Sn, etc. becomes too large, and the crystallinity of the nitride semiconductor tends to deteriorate.

In the present invention, the buffer layer is made of, for example, AlN, GaN, AlGaN or the like at 400 ° C. to 900 ° C.
At 0.5 μm or less, it relaxes the lattice mismatch between the substrate and the nitride semiconductor, or acts as an underlayer for growing the first nitride semiconductor layer with good crystallinity. .

Furthermore, the thickness of the third nitride semiconductor layer is preferably 0.5 μm or less. The more preferable film thickness of the third nitride semiconductor layer is adjusted to 0.2 μm or less, and more preferably 0.15 μm or less. The lower limit is not particularly limited, but 10 angstroms or more, preferably 50
It is desirable to adjust to angstrom or more, and most preferably 100 angstrom or more. The third nitride semiconductor layer is an undoped layer and has a resistivity of usually 0.1.
Since it is as high as Ω · cm or more, when this layer is grown as a thick film layer, on the contrary, Vf tends to be less likely to decrease.

In the present invention, the second superlattice structure is used.
The nitride semiconductor layer may be modulation-doped with an n-type impurity. Further, the first and third nitride semiconductor layers are
For example, as undoped, the resistivity is, for example, 0.1 Ω.
It may be cm or more.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The light emitting device of the present invention has a nitride semiconductor layer having at least a three-layer structure between an active layer and a substrate. First, the first nitride semiconductor layer is undoped in order to grow the second nitride semiconductor layer containing n-type impurities with good crystallinity. If this layer is intentionally doped with impurities, the crystallinity deteriorates and it is difficult to grow the second nitride semiconductor layer with good crystallinity. Next, the second nitride semiconductor layer is doped with an n-type impurity and acts as a contact layer for forming an n electrode having a low resistivity and a high carrier concentration. Therefore, it is desirable that the resistivity of the second nitride semiconductor layer be as small as possible in order to obtain preferable ohmic contact with the n-electrode material, and preferably less than 8 × 10 ⁻³ Ω · cm. Next, the third nitride semiconductor layer is also undoped. This layer is undoped because the crystallinity of the second nitride semiconductor layer having a low resistivity and a high carrier concentration is not so good. Directly on this
When an active layer, a clad layer, or the like is grown, the crystallinity of those layers is also deteriorated. Therefore, an undoped third nitride semiconductor having good crystallinity is interposed between the active layer and the clad layer. Acts as a buffer layer. Further, by interposing an undoped layer having a relatively high resistivity between the active layer and the second nitride semiconductor layer, it is possible to prevent a leak current of the device and increase the reverse breakdown voltage. The carrier concentration of the second nitride semiconductor layer is 3 ×
It tends to be higher than 10 ¹⁸ / cm ³ . The active layer is an undoped nitride semiconductor containing In, preferably I.
A single quantum well structure having a well layer made of nGaN or a multiple quantum well structure is desirable. Examples of the n-type impurities include Group 4 elements, preferably S
i or Ge, and more preferably Si is used.

[0011]

EXAMPLE 1 FIG. 1 is a schematic cross-sectional view showing the structure of an LED element according to an example of the present invention, and the method for manufacturing the element of the present invention will be described below with reference to this figure. .

After the substrate 1 made of sapphire (C surface) is set in the reaction vessel and the inside of the vessel is sufficiently replaced with hydrogen, the temperature of the substrate is raised to 1050 ° C. while flowing hydrogen to clean the substrate. . Substrate 1 includes sapphire C-face, sapphire having R-face and A-face as main surfaces, an insulating substrate such as spinel (MgA1 ₂ O ₄ ), and SiC (6H, 4H, 3C). ), Si, Zn
A semiconductor substrate such as O, GaAs, or GaN can be used.

(Buffer layer 2) Then, the temperature is changed to 510.degree.
Then, hydrogen is used as a carrier gas, ammonia and TMG (trimethylgallium) are used as a source gas, and a buffer layer 2 made of GaN is grown on the substrate 1 to a film thickness of about 200 Å.

(First Nitride Semiconductor Layer 3) Buffer Layer 2
After the growth, only TMG is stopped and the temperature is raised to 1050 ° C. When the temperature reaches 1050 ° C, TM is also used as the source gas.
Using G and ammonia gas, the first nitride semiconductor layer 3 made of undoped GaN is grown to a film thickness of 1.5 μm. The first nitride semiconductor layer 3 is grown at a temperature higher than that of the buffer layer directly grown on the substrate, for example, 900 ° C. to 1100 ° C., and In _X Al _Y Ga _1-XY N (0 ≦ X, 0 ≦ Y, X + Y
≦ 1), and the composition thereof is not particularly limited, but is preferably GaN and Al _X Ga having an X value of 0.2 or less.
_{If it is 1-X} N, it is easy to obtain a nitride semiconductor layer with few crystal defects. The film thickness is not particularly limited, and the film is grown thicker than the buffer layer, and is usually 0.1 μm or more and 20 μm
Grow with the following film thickness. Since this layer is an undoped layer, the resistivity is higher than 0.1 Ω · cm. Also the first
The nitride semiconductor layer 3 is a layer grown at a temperature higher than that of the buffer layer, and therefore is undoped and distinguished from the buffer layer.

(Second Nitride Semiconductor Layer 4) Subsequently, 105
The second nitride semiconductor layer 3 made of Si-doped GaN is grown to a thickness of 3 μm at 0 ° C., using TMG, ammonia gas as the source gas, and silane gas as the impurity gas. This second nitride semiconductor layer 3 is also In _X Al _Y Ga _1-XY N (0 ≦ X, 0 ≦ Y, X as in the first nitride semiconductor layer.
+ Y ≦ 1), and the composition thereof is not particularly limited, but is preferably GaN and Al _X Ga having an X value of 0.2 or less.
_{If it is 1-X} N, it is easy to obtain a nitride semiconductor layer with few crystal defects. The film thickness is not particularly limited, but it is a layer forming the n-electrode, so it is desirable to grow the film with a film thickness of 1 μm or more and 20 μm or less. A wafer on which a second nitride semiconductor layer was similarly grown was prepared using another sapphire substrate not having an element structure, and the resistivity of the second nitride semiconductor layer was measured to be 5 × 10 ^−3. It was Ω · cm.

The second nitride semiconductor layer is formed by laminating two kinds of nitride semiconductor layers having different bandgap energies, or by laminating nitride semiconductor layers having the same composition. Also good. When the superlattice layer is used, the mobility of the second nitride semiconductor layer is increased and the resistivity is further reduced, so that an element having particularly high luminous efficiency can be realized. In the case of the superlattice structure, the film thickness of the nitride semiconductor layer forming the superlattice is 100 Å or less, more preferably 70 Å or less,
Most preferably, it is adjusted to 50 angstroms or less.
Further, in the case of the superlattice structure, the nitride semiconductor layer forming the superlattice may be modulation-doped with Si, Ge, Sn, S or the like. Modulation doping means that the nitride semiconductor layers forming the superlattice layer have different impurity concentrations, and in this case,
One layer may be undoped, that is, undoped. It is preferable that the second nitride semiconductor layer has a superlattice structure in which layers having different bandgap energies are laminated, and one of the nitride semiconductor layers is heavily doped with an n-type impurity, and the other nitride is The semiconductor layer is preferably undoped. In the case of modulation doping, it is desirable that the difference in impurity concentration is one digit or more.

(Third Nitride Semiconductor Layer 5) Then, only silane gas is stopped, and undoped Ga is similarly performed at 1050 ° C.
The third nitride semiconductor layer 5 made of N is grown to a film thickness of 0.15 μm. This third nitride semiconductor layer 5 is also In _x
Al _Y Ga _1-XY N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1), and the composition thereof is not particularly limited, but is preferably G
If aN, Al _X Ga _1-X N with an X value of 0.2 or less, or In _Y Ga _1-Y N with a Y value of 0.1 or less, a nitride semiconductor layer with few crystal defects is easily obtained. When InGaN is grown, cracks can be prevented from forming in the nitride semiconductor layer containing Al when the nitride semiconductor containing Al is grown on it. When the second nitride semiconductor layer is grown as a single nitride semiconductor, the first nitride semiconductor layer, the second nitride semiconductor layer, and the third nitride semiconductor layer have the same composition. It is desirable to grow nitride semiconductors.

(Active layer 6) Next, the temperature is set to 800 ° C., the carrier gas is switched to nitrogen, and TMG and TMI are set.
An undoped In0.4Ga0.6N layer is grown to a thickness of 30 angstroms using (trimethylindium) and ammonia to grow an active layer 6 having a single quantum well structure.

(P-side clad layer 7) Next, the temperature is set to 105.
Raise to 0 ℃, TMG, TMA, ammonia, Cp2Mg
Using (cyclopentadienyl magnesium), a p-side cladding layer 7 made of p-type Al _0.1 Ga _0.9 N doped with 1 × 10 ²⁰ / cm ^{3 of} Mg is grown to a thickness of 0.1 μm. This layer acts as a carrier confinement layer and is a nitride semiconductor containing Al, preferably Al _Y Ga _{1 -Y} N (0 <Y
It is desirable to grow <1), and in order to grow a layer with good crystallinity, a Y value of Al _Y Ga _{1 -Y} N of 0.3 or less is required.
It is desirable to grow the layer to a thickness of 0.5 μm or less.

(P-side contact layer 8) Then 1050 ° C.
Then, using TMG, ammonia, and Cp2Mg,
A p-side contact layer 8 made of p-type GaN doped with x 10 ²⁰ / cm ³ is grown to a film thickness of 0.1 μm. The p-side contact layer 8 is also made of In _X Al _Y Ga _1-XY N (0 ≦ X, 0 ≦ Y, X
+ Y ≦ 1), and the composition thereof is not particularly limited, but when GaN is preferable, a nitride semiconductor layer with few crystal defects can be easily obtained, and a preferable ohmic contact with the p electrode material can be easily obtained.

After the reaction was completed, the temperature was lowered to room temperature, and the wafer was placed in a reaction vessel in a nitrogen atmosphere at 700 ° C.
Annealing is performed at 0 ° C. to further reduce the resistance of the p-type layer.

After the annealing, the wafer is taken out of the reaction container, a mask having a predetermined shape is formed on the surface of the uppermost p-side contact layer 8, and the p-side contact layer side is etched by an RIE (reactive ion etching) device. Done,
As shown in FIG. 1, the surface of the second nitride semiconductor layer 4 is exposed.

After etching, a light-transmitting p-electrode 9 containing Ni and Au having a film thickness of 200 Å is formed on almost the entire surface of the p-side contact layer as the uppermost layer, and Au for bonding is formed on the p-electrode 9. 0.5 for the p-pad electrode 10
It is formed with a film thickness of μm. On the other hand, the surface of the second nitride semiconductor layer 4 exposed by etching contains n containing W and Al.
The electrode 11 is formed. Finally, an insulating film 12 made of SiO ₂ is formed to protect the surface of the p-electrode 9 as shown in FIG. 1, and the wafer is scribed to separate 35.
The LED element is a 0 μm square.

This LED device exhibits pure green light emission of 520 nm at a forward voltage of 20 mA, a buffer layer made of GaN, an n-side contact layer made of Si-doped GaN, and an InG having a single quantum well structure on a sapphire substrate.
Compared to a conventional green light emitting LED in which an active layer made of aN, a p-side clad layer made of Mg-doped AlGaN, and a p-side contact layer made of Mg-doped GaN were sequentially laminated, Vf at 20 mA was 0.1. .About.0.2 V, and the output could be improved by 5% to 10%.

[Embodiment 2] FIG. 2 is a schematic cross-sectional view showing the structure of a laser device according to another embodiment of the present invention, in which the device is cut in a direction perpendicular to the resonance direction of laser light. It shows a structure. The second embodiment will be described below with reference to this drawing.

On the substrate 20 made of sapphire (C plane), the buffer layer 21 is grown to a film thickness of 200 Å in the same manner as in the first embodiment.

(First Nitride Semiconductor Layer 22) After growing the buffer layer 20, the temperature is raised to 1020 ° C. and 1020
The first nitride semiconductor layer 22 made of undoped GaN is grown at a temperature of 5 ° C. to a thickness of 5 μm.

(Second Nitride Semiconductor Layer 23) Then, 1
Silane gas was used as an impurity gas at 020 ° C., and the second nitride semiconductor layer made of n-type GaN doped with Si was 3 μm thick.
Grow with a film thickness of m. The resistivity of this second nitride semiconductor layer was also 5 × 10 ⁻³ Ω · cm.

(Third Nitride Semiconductor Layer 24) Next, the temperature is set to 800 ° C., and TMG, TMI, and ammonia are used to form the third nitride semiconductor layer 24 of undoped In _0.05 Ga _0.95 N at 500 angstroms. To grow.

(N-side clad layer 25) Next, the temperature is set to 102.
TMA, TMG, NH ₃ , Si as raw material gas at 0 ° C
N-type Al doped with Si at 1 × 10 ¹⁷ / cm ³ using H _4
An n-side clad layer having a superlattice structure in which 40 Å of _0.25 Ga _0.75 N layers and 40 Å of undoped GaN layers are alternately laminated is grown. This n-side clad layer acts as a carrier confinement layer and an optical confinement layer.

(N-side light guide layer 26) Subsequently, 1020
An n-side optical guide layer 26 made of n-type GaN doped with Si at 1 × 10 ¹⁹ / cm ³ is grown to a thickness of 0.2 μm at 0 ° C. This n-side light guide layer 26 acts as a light guide layer of an active layer, and it is desirable to grow GaN and InGaN, and it is usually grown to a film thickness of 100 angstroms to 5 μm, and more preferably 200 angstroms to 1 μm. desirable. The n-side light guide layer may be undoped.

(Active layer 27) The temperature is set to 800 ° C., and a well layer made of Si-doped In _0.2 Ga _0.8 N is first grown to have a film thickness of 25 Å. Then, the Si-doped In _0.01
A barrier layer of Ga _0.99 N is grown to a thickness of 50 Å. This operation is repeated twice to finally form a multiple quantum well structure in which well layers are stacked.

(P-side cap layer 28) Next, the temperature is raised to 10
20 ℃, TMG, TMA, ammonia, Cp₂M
and has a larger bandgap energy than the active layer.
1 x 10 Mg²⁰/cm ³Doped Al_0.3Ga
_0.7The p-side cap layer 28 made of N is 300 angstroms
Grow with ROHM film thickness. The p-side cap layer 28 is
It is preferably p-type, but since it is thin, n-type impurities
May be doped to obtain an i-type in which carriers are compensated.
The thickness of the p-side cap layer 28 is 0.1 μm or less, and more preferable.
It is preferably 500 angstroms or less, and most preferably
Adjust to less than 300 Å. 0.1 μm
If grown to a thicker film thickness, the p-side cap layer 28 will be cracked.
A nitride semiconductor layer with good crystallinity because it is easy for racks to enter
Is difficult to grow. In addition, carrier is this energy
It cannot pass through the ghee barrier due to the tunnel effect. A
If the AlGaN having a large composition ratio of 1
The child easily oscillates. For example, A with a Y value of 0.2 or more
l_YGa_1-YIf N, adjust below 500 Å
It is desirable to adjust. Below the film thickness of the p-side cap layer 28
The film thickness is not particularly limited, but a film of 10 angstroms or more
It is desirable to form it with a large thickness.

(P-side light guide layer 29) Subsequently, 1020
At 0 ° C., a p-side optical guide layer 26 made of GaN doped with 1 × 10 ¹⁸ / cm ^{3 of} Mg is grown to a thickness of 0.2 μm. The p-side light guide layer 29, like the n-side light guide layer 26, acts as a light guide layer of the active layer, and is made of GaN and I.
It is desirable to grow nGaN, usually 100 angstrom to 5 μm, and more preferably 200 angstrom to 1 μm. Although the p-side light guide layer is doped with p-type impurities, it may be composed of an undoped nitride semiconductor.

(P-side clad layer 30) Subsequently, 1020
P-type Al doped with Mg at 1 × 10 ²⁰ / cm ^{3 at} ℃
A p-side clad layer 30 having a superlattice structure in which 40 layers of 0.25 Ga0.75 N layers and 40 angstroms of undoped GaN layers are alternately laminated is grown. This p-side clad layer functions as a carrier confinement layer and an optical confinement layer like the n-side clad layer.
By making the side clad layer side a superlattice, the resistance of the p layer is lowered and the threshold value tends to be lowered more easily.

[0036] (p-side contact layer 31) Finally, p-side on the cladding layer 30, 1050 ° C. 2 to Mg at × 10 ²⁰ /
The p-side contact layer 31 made of cm ³ -doped GaN is grown to a thickness of 150 Å.

After the reaction is completed, the temperature is lowered to room temperature, and the wafer is further heated to 700 ° C. in a reaction vessel in a nitrogen atmosphere.
Annealing is performed at 0 ° C. to further reduce the resistance of the p-type impurity-doped layer.

After the annealing, the wafer was taken out from the reaction vessel and, as shown in FIG.
The side contact layer 31 and the p-side cladding layer 30 are etched into a ridge shape having a stripe width of 4 μm. In particular, by forming a layer of a nitride semiconductor layer or more containing Al above the active layer into a ridge shape, the light emission of the active layer is concentrated in the lower part of the ridge, the transverse mode is easily unified, and the threshold value is lowered. Cheap. After forming the ridge, a mask is formed on the surface of the ridge, and as shown in FIG. 2, the surface of the second nitride semiconductor layer 23 on which the n-electrode 34 is to be formed is exposed by making it symmetrical with respect to the striped ridge. Let

Next, a p electrode 32 made of Ni and Au is formed on almost the entire top surface of the ridge of the p-side contact layer 31. On the other hand, the n-electrode 34 made of Ti and Al is formed on almost the entire surface of the stripe-shaped second nitride semiconductor layer 23.
The term "almost entire surface" means an area of 80% or more. In this way, the second nitride semiconductor layer 2 is symmetrical with respect to the p-electrode 32.
It is also very advantageous to expose the third electrode 3 and provide the n-electrode on almost the entire surface of the second layer 23 in order to lower the threshold value. Further, after forming an insulating film 35 made of SiO2 between the p electrode and the n electrode, the p pad electrode 3 made of Au electrically connected to the p electrode 32 through the insulating film 35.
3 is formed.

As described above, the wafer on which the n-electrode and the p-electrode are formed is transferred to the polishing apparatus, and the sapphire substrate 20 on the side where the nitride semiconductor is not formed is lapped by using the diamond abrasive. The thickness of the substrate is 50 μm. After lapping, the substrate surface is mirror-finished by polishing with 1 μm with a finer polishing agent.

After polishing the substrate, scribe the polishing surface side,
Cleavage is performed in a bar shape in a direction perpendicular to the striped electrode, and a resonator is formed on the cleaved surface. SiO ₂ and TiO ₂ on the cavity surface
A dielectric multi-layered film is formed, and finally the bar is cut in the direction parallel to the p-electrode 32 to obtain a laser element. When this device was installed on a heat sink and laser oscillation was attempted at room temperature, the threshold current density was 2.5 kA / c at room temperature.
At m ² and a threshold voltage of 4.0 V, continuous oscillation with an oscillation wavelength of 405 nm was confirmed, and it showed a life of 500 hours or more, which was 10 times or more that of a conventional nitride semiconductor laser device.

[Third Embodiment] In the first embodiment, when the third nitride semiconductor layer 5 is grown, the temperature is set to 800.degree.
Undoped In _0.05 G using G, TMI, and ammonia
An LED device was obtained in the same manner as in Example 1 except that the a _0.95 N layer was grown to a film thickness of 200 Å.
An element having substantially the same characteristics as in Example 1 was obtained.

[0043]

As described above, in the device of the present invention, the undoped first nitride semiconductor layer between the active layer and the substrate is doped with the n-type impurity to form the second nitride semiconductor. Therefore, the second nitride semiconductor layer doped with the n-type impurity can be grown as a thick film with good crystallinity. Further, the undoped third nitride semiconductor serves as an underlayer having good crystallinity for the nitride semiconductor layer grown on the layer. Therefore, the resistivity of the second nitride semiconductor layer can be reduced and the carrier concentration is increased, so that a very efficient nitride semiconductor element can be realized. As described above, according to the present invention, since a light emitting element having a low Vf and a threshold value can be realized, the amount of heat generated by the element can be reduced, and an element with improved reliability can be provided.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of an LED element according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view showing the structure of a laser device according to another embodiment of the present invention.

[Explanation of symbols]

1, 20 ... Substrate 2, 21 ... Buffer layer 3, 22 ... First nitride semiconductor layer 4, 23 ... Second nitride semiconductor layer 5, 24 ... Third nitride semiconductor layer 6, 27 ... Active layer 7, 30 ... P-side clad layer 8, 31 ... P-side contact layer 25 ... n-side light guide layer 26 ... N-side clad layer 28 ... p-side cap layer 29 ... p-side light guide layer 9, 32 ... p-electrode 10, 33 ... p pad electrode 11, 34 ... N-electrode 35 ... Insulating film

   ─────────────────────────────────────────────────── ─── Continued front page       (56) References JP-A-9-97921 (JP, A)                 JP-A-9-27640 (JP, A)                 JP-A-7-249795 (JP, A)                 JP-A-9-129930 (JP, A)                 Japanese Patent Laid-Open No. 7-302929 (JP, A)                 JP-A-9-293935 (JP, A)                 JP-A-61-221726 (JP, A)                 Japanese Patent Laid-Open No. 10-303458 (JP, A)                 Japanese Patent Laid-Open No. 8-8274 (JP, A)

Claims (9)

(57) [Claims] 1. An undoped first nitride semiconductor layer, an n-conductivity type second nitride semiconductor layer doped with an n-type impurity, and an undoped one in order from the substrate side between the substrate and the active layer. And a buffer layer grown between the substrate and the first nitride semiconductor layer at a temperature lower than that of the first nitride semiconductor layer. The device is characterized in that the second nitride semiconductor layer has a superlattice structure, an n electrode is formed on the second nitride semiconductor layer, and the third nitride semiconductor layer is InGaN. And a nitride semiconductor light emitting device. 2. The nitride semiconductor light emission according to claim 1, wherein the third nitride semiconductor layer is In _y Ga _1-y N having an In mixed crystal ratio y of 0.1 or less. element. 3. An undoped first nitride semiconductor layer, an n-conductivity type second nitride semiconductor layer doped with an n-type impurity, and an undoped layer in order from the substrate side between the substrate and the active layer. And a buffer layer grown between the substrate and the first nitride semiconductor layer at a temperature lower than that of the first nitride semiconductor layer. In the device, the second nitride semiconductor layer has a superlattice structure, an n electrode is formed on the second nitride semiconductor layer, and the resistivity of the second nitride semiconductor layer is 8 × 10. ^-3 Ω ・ cm
It is less than 1 × 10 ⁻⁵ Ω · cm and is less than 1 × 10 ⁻⁵ Ω · cm, and the first nitride semiconductor layer is AlGaN. 4. The nitride semiconductor light emitting device according to claim 3, wherein the first nitride semiconductor layer is Al _X Ga _{1 -X} N having an X value of 0.2 or less. 5. An undoped first nitride semiconductor layer, an n-conductivity type second nitride semiconductor layer doped with an n-type impurity, and an n-type impurity-doped second nitride semiconductor layer in order from the substrate side between the substrate and the active layer. A third nitride semiconductor layer having a resistivity higher than that of the second nitride semiconductor layer, and a temperature lower than that of the first nitride semiconductor layer between the substrate and the first nitride semiconductor layer. A second semiconductor layer having a superlattice structure, an n-electrode is formed on the second semiconductor layer, and the second semiconductor layer has a buffer layer grown on the second semiconductor layer. The resistivity of the nitride semiconductor layer is 8 × 10 ^-3 Ω · cm
A nitride semiconductor light-emitting device, characterized in that it is less than 1 × 10 ⁻⁵ Ω · cm. 6. The nitride semiconductor light emitting device according to claim 5, wherein the third nitride semiconductor layer is GaN or InGaN. 7. The method according to claim 5, wherein the first nitride semiconductor layer is GaN or AlGaN.
The nitride semiconductor light emitting device according to claim 1. 8. The film thickness of the third nitride semiconductor layer is 0.
It is 5 micrometers or less, The nitride semiconductor light-emitting device as described in any one of Claims 1-7 characterized by the above-mentioned. 9. The nitride according to claim 1, wherein the second nitride semiconductor layer having the superlattice structure is modulation-doped with an n-type impurity. Semiconductor light emitting device.